Aerofoil for aeroplanes



A. A. HOLLE.

AEROFOIL FOR AEROPLANES.

APPLICATION FILED AUG.I1. I919.

Patented May 31, 1921. 2

.FFICE. v

annxaivnnn ALBERT EOLLE, or wns'rmqmsrna, Lennon, ENGLAND.

' ororr. non annormnns.

Home, a subject of the Queen of the Netherlands, residing at 19 Half Moon street, in

a the city. of Westminster, administrative county of London, have invented certain new and useful Improvements in Aerofolls for Aeroplanes, of which the following is a specification.

This invention relates to the wings or aerofoils of aeroplanes and has for its object to obtain automatic longitudinal stability under variations of the angle of incidence relatively to the air without the use of small auxiliary 'aerofoils or the like.

The longitudinal instability *of a cambered aerofoil arises from an unstable variation of the distribution of pressure due'to the changes in the level or angle at which the air is divided at theleading edge ofthe aerofoil or from a combination of both chan es, and to the formation-at-al1 angles -but t e one to which the curvature of the aerofoil is best suited-01? a region of dead air which constitutesywhat is in eflect an artificial extension of the nose of 'the aero foil, which gives rise to'an alteration in the air flow. For instance, at lesser angles than the optimum angle -for the curvature, as when struck by. a downward gust or when the angle of fli'ht is accidently reduced from any cause, t 1e air flow is divided at a point above and in front of the leading edge of the aerofoil, and inversely when struck by an upward st or when the angle of flight is accident y increased, the air flow is divided at a point below the leading edge. In the former'case the dead air nose,'as I will term it, extends above the leading edge and presents a flatter angle of entry to the air flow, which causes theair tofstrike the aerofoil at a lesser angle where the degree of curvature of the aerofoil is less than at the leading edge. This creates a less intensive vacuum and causes a considerable portion of the upper surface of the aerofoil ad-- jacent to its eading edge to be under-a positive downward and backward pressure, which results in thecenter of-pressure moving nearer to the trailing edge of the aerofoil. In the latter case, when the angle is greater than the optimum angle for the curvature, the dead air nose extends below the leading edge of the aerofoil and the air flow is directed upward at a steeper angle Specification of Letters Patent.

, By controlling thisfdead air nose or leading Patented Ma'y 31, 1921.

- Application nleanu ust 11, 1919. Serial no. 316,919.

which brings forward. I v

nose by reducing or'regulating or by both means com.-

bined; the heaping up of air at the leadingthe center of pressure more v edge of the aerofoil astable variation of the distribution of In addition to which it makes'it' possible to adopt a single spar system of construction .for the aerofoil.

- I attain the object of this invention by maklng the leading or forward part of the aerofoil flexible in such a mannerthat, when the leading edge is under excessive downward pressure the nose or leading edge flexes downward and slightly rearward whereby the camber. of the upper surface inpressure can be obtained. 1 v

creases and the concavity of the under surface decreases so that the angle of entry becomes steeper and the stratum of air swept by the aerofoil is divided and inversely, when said nose or leadin edge is under excessive upward pressure, sai

edge flexes upward and slightly forwar upper surface decreasesandv the curvature of the under surface of the leading part is increased so that the angle of flatter and the stratum of 'air swept by the aerofoil is divided at a higher level which results in'the dead Fig. 3 showing the leading-edge under the influence of a maxlmum of excessive downward pressure. and Figs. 4 and 5 are broken views-in side elevation and plan respectively showing-41y way of example-one method of carrying this invention into practice. 4 Throughout the views similar parts are marked with like letters of reference.

whereby the camber of the position under load,

76 ata lower level, v

entry becomes I air? formation underthe leading edge being reduced.

According to the present invention the forward part w of the aerofoil is made fiexible within certainlimits the upper surface, being eambered in the usual manner and the undersurface when the aerofoil is not 1111- der load being also slightly cainbered i. e.

of slightly convex form. When the aerofoil is under load the convexity of the under surface becomes a concavity and when there is excessive as sure above its nose or leading edge 00 it begdeflected down ward and slightly rearward which will increase the camber of its surface and decrease the concavity of its under surface, and when there is excessive pressure under its nose or leadin edge it willbe deflected upward and slig tly. forward which will decrease the, camber of its upper surface and increase the curvature of its under surface at its leading part, the result being that the forward motion of the wing will give it its 0 timum shape by reason ofthe-pressure distribution resulting from the forward motion of the correct angle. It will be appreciated that during excessive downward pressure the concavity of the under surface of the forward part will gradually disappear and become convex as shown in Fig. 3 due to the increased negative pressure 25 created under it.

In the construction shown in Figs. 4: and '5 the main part 00 of the aerofoil is of the usualrigid construction and the element 02 forming the nose of the leading part 00 of tliejaerofoil is supported b a series of elasticfelements I) carried eit er by the main spar y as shown, or to the longitudinal ribs or formers '2, the upper surface 0 being supported by means of a series of flexible mem-' bers c which extend between the main spar and the element a to both of which they are fixed and the under surface to being supported by means of a series of flexible members (2 which extendbetween said main 40 spar y and said element a being fixed to the latter and free to slide in relation to the former. Theshape of the members 0 and d is such as to make the upper and under surfaces of the leading or forward part a" conform to 1 the general curvature of the aerofoil when-flying at the normal angle of incidence and under normal load.

To limit the movements of the elastic elements b and therefore the degree of flexibility of the leading edge stops such as e, e

are provided which can conveniently be'carried by the adjacent longitudinal ribs or formers 2. When it is desired to vary the degree ,of flexibility of the elastic members 6 during flight the ositions of the stops 6 are made adjustable 1n relation to said members by means "of any suitable mechanical device. v

- It will be appreciated that the difference between the tabilityaflordedby the present invention and that of the hitherto known stable wing is that in said'known' type of stable wing in which the instability over difl'erent portions are made to negative each at others action there is a constant torsional ar ner stress inthe wing tending'to deform the wing, while in a wing constructed according to the present invention there is an antitorsional stress generated as soon as the pressure distribution varies owing to changes in the angle of incidence which tends to preserve the shape of the wing and rehe'ves the spar of any torsional stress which makes for simplification of design and reduction of weight.

ll claim:

1'. lln an aerofoil for aeroplanes, the combination of a rigid main part which comprises a main spar, a series of rigid ribs or formers carried by said spar the forward so ends of which do not extend as far as the nose or leading edge, and covering surfaces carried by said ribs or formers and extend ing between said mainspar and the rear or trailing edges; and a flexible forward part comprising a series of elastic members-carried by the mainspar, a rigid nose carried by said elastic members, a series of flexible elements extending between and carried by the main spar and thenose, a series of flexie0 ble elements carried by the nose and extending between said nose and said main spar,

and covering surfaces carried by said flexible elements.

flexible elements extending between and carried by the main spar an the nose, a series of flexible elements carried by the nose and extendin between said nose and said main spar, an coveringsurfaces carried by said elements; and means j for limiting the amount of movement of theelastic members, 3. In an aerofoil for aeroplanes, the'com bination of a rigid main part which comrises a main spar, a series of rigid ribs or ormers carried by said spar the forward ends of which do not extend as far as the nose or leading edge, and covering surfaces carried by said ribs or formers and extend- 12b ing between said main spar and the rear or trailing edge; and a flexible forward part comprising a series of elastic members carried by the main spar, a rigid nose carried b said elastic members, a series-of flexible 1125 eliements extending between and carried-by. the main spar and-the nose, a series of flexible elements carried by the nose "and extending-between said nose and said main spar, and covering surfaces carried by said 'ele we ments; and means for varying thedegree of flexibility of the forward part of the aerofoil.

4. An aerofoil for aeroplanes comprising a rigid main part which consists of a main spar, a series of rigid ribs or formers attached to said spar the forward ends of which do not extend as far as the nose or leading edge, and covering surfaces carried by said ribs or formers and extending between said main spar and the rear or trailing edge; and a flexible part consisting of a series of elastic members carried by the main spar, a rigid nose carried by said elastic members, a series of flexible elements extending between and attached to the main spar and the nose, a series of, flexible elements carried by the nose and extending be tween said nose andsaid main spar, and,

flexible coverings carried by said flexible elements; amount of movement of the elastic members and thereby varying the degree of flexibility of the forward part of the aerofoil.

5. An aerofoil for aeroplanes comprising a rigid main part which consists. of a main spar, a series of rigid ribs or formers attached to said spar the forward ends of which do not extend as far as the nose or leading edge, and covering surfaces carried by said ribs or formers and extending be and means for limiting the ribs or formers forward of the main spar,-

and means for adjusting the relative positions of said stops.

6. The combination in an aerofoil for aero planes of a main spar, a series of rigid ribs or formers carried by said spar covering surfaces carried by said rigid ribs or formers and extending between said main spar and the rear or trailing edge, a series of elastic members carried a rigid nose carried by said elastic members, a series of upper flexible elements extending between and fixed to said main spar and said nose, a series of under flexible elements extending between said nose and said spar and fixed to said nose, coverings carried by said flexible elements and means for varying the degree of flexibility of said elastic members.

ALEXANDER ALBERT HOLLE.

by said main spar, 

